Process of retanning leather with a condensation product of sulfones of monohydric phenols, non-aromatic amines and formaldehyde



PROCE 69F RETANNENG LEATHER WITH A CONDENSATEON PlRflD UCT F SULFQNES OFMQNUHYDRIC PHENGLS, NONARGMATIC AMINES AND FQRMALDEHYDE Martin Meister,Leverltusen-Vl iesdorf, and Gustav Maiithe, ()pladen, Germany, assignorsto Farbenfabrilren Bayer Alrtiengesellschaft, Leverkusen, Germany, acorporation of Germany No Drawing. Application duly 7, 1953, Serial No.366,612

Claims priority, application Germany July 12, 1952 4 Claims. (Cl.8-94.21)

The present invention relates to a new retanning process using salts ofcondensation products obtained from sulfones of monohydric phenols,non-aromatic bases and formaldehyde.

In our copehding application Ser. No. 295,558, filed June 25, 1952, andnow U. S. Patent No. 2,733,977, we have described a new tanning processconsisting inter alia in retanning and, if desired, neutralizing tannedleather or pretanned hides with condensation products of polyphencls,aromatic, non-aromatic amines orvammonia, as well as their salts, andaldehydes. These condensation products, which are obtained bycondensation of more than 1 mol of polyphenols with 1 mol of amine oramine hydrochloride, are self-tannins with excellent tanning properties;they may be used to prepare commercial leather from animal hides and canbe analysed by the hide powder analysis using 4 grams of pure tannin perliter.

The importance of the above retanning process consists in that theanionic tannins (the previously used tannins and auxiliary tannins ofnatural and/ or synthetic origin are of anionic nature), which are fixedin the leather or the hide substance, are converted to completelyinsoluble compounds by the cationic tannins of the invention. Thesecationic tannins impart to the leather an increase in weight and volumewhich could not be achieved up to the present. Furthermore, tannedleather of a poor filling effect is levelled up by said tannins. Thesubstantially phenolic character of these tannins guarantees a uniformpenetration into the hide and leather substance without the undesiredcase-hardening occurring.

In accordance with the invention we have found that the salts of thecondensation products of the'sulfones containing monohydric phenols withprimary and secondary non-aromatic bases and formaldehyde can be adoptedto the process described in our copending application Ser. No. 295,558,filed June 25, 1952, now U. S. Patent No. 2,733,977. This eiiect is themore surprising since these condensation products show no capacity ofprecipitating gelatine or only to an immaterial degree, and theirtanning effect on pelts prepared for tanning is poor.

The manufacturing process of the condensation products of sulfones andamine salts and the stability of these products to excess aldehyde andhigher temperatures is described in our copending application Ser. No.354,656, filed May 12, 1953. Higher molecular weight products with alower diffusibility into the hide and leather are not formed during theprocess. The very low viscous solutions guarantee a rapid penetrationinto the leather substance.

The condensation products obtained from sulfones and amine salts areamphoteric in character, i. e. they are soluble in both alkalies andacids. They are generally insoluble around the neutral point. Stronglybasic condensation products containing 2 amino groups in each nucleusare sometimes soluble upon addition of acids. Also organic acids mayform salts. These condensation products, which Patented Oct. 8, 1957 aresalt-like cationic compounds, precipitate anionic compounds such astannings, auxiliary tannins, dyestuffs and sulfonated oils practicallycompletely.

Leather is retanned with these condensation products obtained fromsulfones and amine salts in quantities up to 25% in a usual tan liquor.Finally, the leather is neutralized with ammonia, especially when thebases are insoluble. This allows of exhausting the tan liquorscompletely and of incorporating higher percentages of retanhing agentsinto the leather whereupon an amazing increase in thickness of theleather is achieved. Light leather may be retanned by the brushingprocess, heavy leather by drurn-tanning or pit-tanning.

A marked increase in thickness can be ascertained after the usualprocessing and drying of the leather. Condensation products containing 1amino group in each nucleus lead to an increaseof 20%, productscontaining 2 amino groups in each nucleus to a still higher increase. Inspite of the increased filling effect the mellow handle of the leatheris preserved, the color of the leather is lightened, the adsor'btivepower for fats and the stability to light, in particular of leathertanned with vegetable tannins, is improved. The substantially improveddyeability or leather retanned by the herein described process isstriking.

it is within the scope of the invention to retan leather tanned withmineral tannins, especially chrome leather, with the condensationproducts obtained from sulfones and amine salts. 1he filling effect ofthe leather is increased without the typical chrome character and thefine appearance of the grain being essentially altered. it is aremarkable feature of the invention that the chrome salts can be appliedin combination with organic cationic condensation products. the salts,however, must be tested in advance for their compatibility since thesulfates of the organic cationic products are, in most cases, moredift'iculily soluble than the chlorides, and the chrome tanning saltssold on the marieet are suliates throughout. in such single bath tanningprocesses the chrome component is frequently masked.

'lhe condensation products of sulfones and amine salts employedaccording [O the invention for retanningleather can be admixed with thecationic tannins described in our copenoing applications Ser. NO.241,093, hied August 13, 1951, now abandoned, and Ser. No. 351,460,riled January 15, i955, in all proportions; these condensation productsimprove the stability or said cationic tannins during tanning. We havesurprisingly found that up to '/u2 u/o of these self-tannins can bereplaced by the condensation products or sulfones and amine salts, whichare contemplated originally for retanning processes, without theseii'ianning capacity of the mixtures as compared with the self-tanninsbeing substantially aitected. Mixtures or the condensation productsobtained troin sulfones and amine salts and the cationic tanninsdescribed in said copending applications, which may be used assell-tannins, are exceiientiy suited for retanning leather tanned withorganic and mineral tannins.

iiie following examples illustrate the invention, the parts being byweight, it not otherwise stated.

tsxzmzpte 1.luu parts (calculated on the shavers weight) of a chromecalf leather tanned in the usual manner with 3 parts of chrome oxide inthe form of a commercial trivalent basic chrome salt and shaved to athickness of 1.6 mm. are rinsed in flowing cold water for 30 minutesafter accurately measuring the thickness of the leather at variousplaces, and then milled in 200-250 parts of cold water.

A solution of 1 part of the dry substance of the cationic condensationproduct (hereinafter called retanning agent),

0 prepared by the process of our copending application Ser. No. 354,656,filed May 12, 1953, from 1 mol of 3 4.4'-dihydroxydiphenylsulfone, 2mols of ethanol amine and 2 mols of formaldehyde and adjusted to a pH ofabout 3.5 with hydrochloric acid, in parts by volume of water is addedin 2 portions at an interval of 5 minutes. [The retanning agent isprepared by mixing the 4,4- dihydroxy-diphenyl-sulfone, with stirring,with the ethanolamine, then slowly reacting the resulting warm mixturewith the formaldehyde solution) as an exothermic reaction occurs. Afterheating the homogeneous mixture in a boiling water bath for 1 hour, thewater insoluble base is dissolved in 120-130 cc. of concentratedhydrochl ric acid at about 70 C. If the addition compound of sulfone andamine crystallizes and solidifies prematurely. the mixture isnevertheless heated with the aldehyde whereupon dissolution occursgradually] After milling for 30 minutes the tanning solution shows a pHof about 4.6. Upon addition of minor quantities of a dilute ammoniasolution the t nning solution becomes slightly turbid due to precipitting free portions of retanning agent. To exhaust the tanning solutionin 23 portions ammonia solution (about 5%) is added in 2-4 portions unil the pH value of the tanning solution has increased to 5.86.0. Theleather is subsequently milled for another 30-45 minutes. No turbidityoccurs any longer in the tanning solution upon addition of furtherquantities of dilute ammonia. that means the retanning agent has beenabsorbed.

The leather is trestled over night and thereafter subjected to the usualaftertreatment. By drying a sample after normal fat-liquoring in thisnon-colored condition a leather is obtained which is distinguished fromnon retanned chrome leather by better filling properties, a softerhandle and a character which could not be a hieved by a process usingvegetable retanning agents in higher quantitics. The fine surface lusterof the leather is especially striking. By dyeing the non-dried leatheraccording to the methods usually applied in dyeing chrome leather with lpart of a comm rcial acid leather dyestuff the leather subjected toaftertreatment with the retanning agent assumes a markedly deeper andmore covered shade than a non-retanned chrrme leather which, otherwise,has been fat-liquored and dyed in equal manner and originates from a comarable position of the same hide. The dried, colored leather is measuredwith the caliper and the thus ascertained values are compared with thefigures determined in the wet state after shaving the leather. Thenon-ret nncd leather shows a l ss of thickness of 2.35% whereas theleather treated with the retanning shows an increase of thicknessof0.1%.

Examvle 2.100 p rts of the shaved chrome leather are treated with 3parts of the above retanning agent (Example 1) in the manner describedin Exam le 1. After dyeing with 1 part of a mixture of acid andsubstantive dyestuffs this leather showed an essentially deeper, morecovered shade as compared with a non-retanned leather which originatesfrom a comparable position of the same hide. In a diagonal cut it can beseen that the dyestu f penetrates into the retanned leather to anessentially lesser degree and is substantially fixed in the top layersof the grain and flesh side. By measuring the thickness of the leatheras described above a loss of thickness of 2.0% is ascertained in thecase of the nonretanned leather whereas the retanned leather shows anincrease of thickness of 6.3%.

Example 3. 1O0 parts of chrome leather, as described in Example 1 areretanned in the manner described in Example 1 with a solution of 3 partsof the dry substance of a retanning agent (in 25 parts by volume ofwater), which was obtained as follows: 3 parts of the dry substanceof'the tannin prepared by the process of our copending application Ser.No. 241,693, filed Aug st 13, 1951 (Example 33) fr m res rcin l. ammnium chl ride and formaldehyde. are mixed with 7 parts of a dry substance of the condensation product, described in Ex mnle 1, from4.4-dihydroxy-diphenylsulfone, ethanol amine and formaldehyde, which wasadjusted to a pH of about 3.5 with hydrochloric acid, and water is addedto the mixture until a sirup capable of being easily poured has formed.Following is the procedure for preparing the tannins of Example 33,application S. N. 241,693:

102 cc. of formaldehyde solution 30% are added to the solution of 18grams of ammonium chloride and 110 grams of resorcinol in 60 cc. ofWater at room temperature. Within a few minutes the temperature risesabove C.; the mixture is then heated for further 1% hours in the boilingwater bath.

With 126 grams of pyrogallol the condensation proceeds likewise stronglyexothermic. As the pyrogallol tends to crystallize prematurely, thealdehyde is added at 45 C.; the temperature rises to the boiling pointof the reaction mixture. The mixture is heated for further 1% hours inthe boiling water bath.

A mixture of e. g. 55 grams of resorcinol and 63 grams of pyrogallolshows quite a similar behaviour. The aldehyde can be added at 20 to 25C.

The condensation of grams of catechol or grams of brenzoeF instead ofthe above-mentioned 110 I grams of resorcinol proceeds only weaklyexothermic.

The aldehyde is added at 35 C., and the mixture is heated in the boilingwater bath; there the reaction mixture comes to boil for a short time.It is heated for 2 /2 hours in the boiling water bath.

By decreasing the quantity of the ammonium chloride and using the samequantity of aldehyde more viscous, higher molecular, water-solublecondensation products are obtained.

The resorcinol condensation product, neutralized with a little ammonia,shows the following analytical values:

Concentration 47.8%. Tannins 34.3%. Percentage of pure tannin in drysubstance 71.7.

Acid number pH value 6.25.

Weight of sample 12 grams=4.1 grams of pure tannin per liter.

With the corresponding quantities of ammonium bromide the condensationreactions proceed practically in the same way as those described above.The aldehyde is added at the temperature at which one of the reactingagents begins to separate, after complete dissolution had been effectedat higher temperature. If necessary, the reaction may be restrained byshortly cooling with water. After fat-liquoring and dyeing the non-dyedleather is distinguished from a non-retanned chrome leather by a greaterfilling effect, a beautiful surface luster and a softer handle. Thechrome leather color has disappeared, the leather has a yellowish brownappearance and a character like the leather retanned with vegetabletannins.

By dyeing with 1 part of an acid commercial dyestuif the retannedleather assumes an essentially deeper, more covered sh de than thenon-retanned leather. The measuring of the thickness of the leather asdescribed in Example 1 shows that the non-retanned leather has decreasedin thickness by 2.0% where-as the retanned leather has increased inthickness by 19.4%.

Example 4.A piece of cow-hide tanned with a mixture of vegetable andsynthetic tannins in a series of pits, which had not yet been subjectedto the usual drum tanning, is set out well, rinsed with flowing coldwater for 30 minutes, set out once more and divided into 2 approximatelyequally large pieces designated 1 and II. The weight of each of thesepieces is determined and the thickness is accurately measured at variousplaces with the caliper.

100 parts (referred to the sammied weight) of the piece designated l aremilled in a solution of 1.2 parts of acetic acid (30%) in 300 parts byvolume of water of 20 C. for 4O minutes. The pH value of the solution isatabout 4.0-4.2. The leather I is then tanned in 300 parts by volume offresh solution of 20 C. containing 3 parts of the dry substance of theretanning agent named in Example 1, prepared from 4.4-dihydroxydiphenylsulfone, ethanol amine and formaldehyde, by dissolving the said quantityof retanning agent in about 30 parts by volume of water and introducingthe solution in two portions at an interval of minutes. After a runningtime of 45 minutes the tanning solution is adjusted to a pH of about 5.0within 20 minutes by addition of dilute ammonia solution (about 5%) inportions. The leather is trestled over night, shortly rinsed thefollowing morning and milled in 300 parts by volume of tanning solutionof 45 C. containing 4 parts of a customary fat-liquoring mixture for 70minutes. After drying a very fine, pliable and mellow leather of goodfeel and yellowish-brown color is obtained.

For comparison 100 parts of the leather designated H are retanned by theusual method as follows: The leather is fat-liquored in 300 parts byvolume of water of 45 C. with 4 parts of the fat-liquoring mixture,which was employed for the leather 1, for 70 minutes and 3 parts of thepure tannin sumac extract dissolved in twice the volume of water isadded to the same solution in two portions at an interval of 5 minutes.One hour after addition of the pure tannin the solution shows a pH ofabout 4.6.

Due to the poor exhaustion of the solution 0.2 part of formic acid (85%)is added to the tanning solution. After milling for 2 hours the solutionhas a pH of about 3.8. The leather is then removed from the solution anddried as usual. It is substantially harder, the feel is less good androugher than the leather 1, the color is flatter and more reddish.

The following table shows comparative figures regarding the increase inthickness, the proportion of dry weight of the fully tanned leather tothe shaved weight, the residual fat content of the liquoring solutionand the content of substances capable of being washed out.

Example 5.100 parts (calculated on the sammied weight) of a vache soleleather tanned with vegetable and synthetic tannins at 12 B. which wasshortly rinsed, set out, pressed off and suspended in the air, arepreliminarily milled in the hot air-drum at about 35-40 C. for minutes.

1.5 parts of diluted technical acetic acid (1210) are added and theleather is milled at 35-40 C. for further 10 minutes. Thereupon asolution of 5 parts of the retanning agent described in Example 1 isadded in the form of a solution in 10 times the quantity of water in 2portions at an interval o-f 10 minutes and the leather is milled for 1hour while cold air is introduced from time to time. After this time thetannin has penetrated into the leather. A solution of 0.5 part of sodiumacetate dissolved in 10 times the quantity of water is added and a thesolution is milled into the leather within minutes. The leather is thenstored for 40 hours, fat-liquored with an oxidation inhibiting leatheroil and carefully dried in a dark room.

The outside appearance of the leather is only slightly diferent from anon-retanned leather which has been oiled off and dried in the samemanner and originates from the same hide.

In spite of the additional quantity of the retanning agent incorporatedinto the retanned leather the content of substances capable of beingwashed out totals to 10.3%

whereas the non-retanned leather shows a content of these substances of13.6%. The content of organic substances capable of being washed out is9.6% and 13.1% respectively.

Example 6.-l00 parts each (calculated on the sammied weight) of a goatskin tanned with 25 parts of pure tannin of a Vegetable mixtureconsisting of equal parts of pure tannin of cold dissolving quebrachoextract and mimosa bark extract are retanned as follows:

Leather 1 with 5 parts of the dry substance of the condensation product,employed in Example 1 and adiusted with hydrochloric acid, which isprepared from 4.4-dihydroxy diphenyl sulfone, ethanol amine andformaldehyde.

Leather 2 with 10 parts of the dry substance of the aforesaid retanningagent.

Leather 3 with 20 parts of the dry substance of the aforesaid retainingagent.

Leather 4 with 5 parts of the dry substance of the retanning agentdescribed in Example 3, which consists of a mixture of the condensationproduct prepared from 4.4'-dihydroxydiphenyl sulfone, ethanol amine andformaldehyde, and the condensation product prepared from resorcinol,ammonium chloride and formaldehyde.

Leather 5 with 10 parts of the aforesaid mixture.

Leather 6 with 20 parts of the aforesaid mixture.

Leather 7 with 10 parts of the dry substance of a vegetable mixtureconsisting of cold dissolving quebracho extract, mimosa bark extract,chestnut extract, myrabolatn extract and valex powder (30:30:30:5:5parts of pure tannin).

Leather 8 with 30 parts of the dry substance of the aforesaid mixture.

Leather 9 is not retanned for comparison.

The pieces of leather 1-6 are retanned as follows: each piece of leatheris shortly rinsed and well sammied. The thickness of each piece ofleather is measured at 10 places. Each leather is then placed in asolution of about 250-300 parts of cold water.

The retanning agents are added at intervals of 15 minutes whilecontinuously milling and the solution is circulated for totally twohours. After measuring the pH value of the solution is adjusted to about5.8-6.2 by careful addition of ammonia (about 5%). This pH value isreached within about 30 minutes. After the ammonia has been added thesolution is circulated for a further 30 minutes and the pieces ofleather are then removed. After shortly rinsing each leather is sammied,oiled off from the grain with a suifonated commercial fatliquoring oiland dried. The leather 7 and 8 are retanned in the usual manner andrinsed, seat out, fat-liquored and dried as described above. Leather 9is rinsed in the same manner without retanning, set out, fat-liquoredand dried.

After oiling the thickness of the leather is measured at 10 places whilestill wet. The increase in thickness over the measurements in the wetstate before retanning'is indicated in the following table:

Leather N o.

The pieces of leather Nos. 1-6 retanned according to the hereindescribed process have a good filling effect and a uniform, beautiful,light color. The retanning agent is Well fixed, even when employed invery great quantities.

Leather 7 has essentially poorer filling properties, the fixation of thetannin is good. The filling effect of leather No. 8 is also markedlyinferior to. that of the piecs 1-6. The fixation of the tannin is poor,the leather color has an unsettled appearance, especially at and nearthe margins. Leather No. 9-gives a markedly flat and dead impression.

Example 7.100 parts each of the goat skin tanned with the vegetabletannin employed in Example 6 are retanned in 250 parts by volume ofwater as follows:

Leather 1 is retanned with 2 parts of the dry substance of a mixture ofretanning agents, which consists of equal parts of the dry substance ofthe retanning agent, employed in Example 1, consisting of4.4-dihydroxydiphenylsulfone, ethanol amine and formaldehyde, and theretanning agent prepared from catechol, ethylene diamine andformaldehyde according to Example 23 of our copending application Ser.No. 241,693, filed August 13, 1951. Following is the procedure given inthat example: 100 cc. of formaldehyde solution 30% are added to thesolution of 110 grams of catechol, 80 cc. of water, 30 grams of ethylenediamine and 42 to 63 cc. of concentrated hydrochloric acid; the reactionis moderately exothermic; the smell of aldehyde soon disappears. Thereaction mixture is heated for one hour in the boiling water bath.

Leather 2 is retanned with parts of the dry substance of the aforesaidmixture of retanning agents.

Leather 3 is retanned with 2 parts of the dry substance of a mixture ofretanning agents consisting of equal parts of the dry substance of theretanning agents employed in Example 1, which is prepared from 4.4-dihydroxydiphenylsulfone, ethanol amine and formaldehyde, and theretanning agent prepared from catechol, morpholine and formaldehydeaccording to our copending application Ser. No. 241,693, filed August13, 1951 (Example 26, third passage) by the following procedure: Thesolution of 44 grams of morpholine, 50 cc. of water, 41 cc. ofconcentrated hydrochloric acid and 110, grams of catechol which shouldshow only weakly congo-acid reaction is mixed at 20 C. with 101 cc. offormaldehyde solution 30%. The temperature rises in the beginningslowly, afterwards more quickly towards 90 C. The reaction mixture isheated for 4-5 hours in the boiling water bath. The condensation productobtained is water-soluble in every proportion.

Leather 4 is retanned with 5 parts of the dry substance of the aforesaidmixture of retanning agents.

Leather 5 is not retanned.

The retanning process and further treatment is carried out as describedin Example 6. After oiling off the thickness of the leather is measuredat places while the leather is still wet. The increase in thickness overthe measurements before retanning is indicated in the following table:

Increase in thickness, percent Leather N o.

by conventional methods. The pieces ofleather are rinsed in flowingwater for some minutes and suspended in solu-' tions of the followingcomposition for two days each (about 8 parts by volume of the solutionsare employed per 1 part of leather (referred to the sammied weight)Leather 1 in a solution of 10 parts of dry substance of the mixture ofretanning agents, described in Example 3, in 1000 parts by volume ofwater.

Leather 2 in a solution of 20 parts of the dry substance of the sameretanning agent in 1000 parts by volume of water.

Leather 3 in a solution of 40 parts of the dry substance of the sameretanning agent in 100 parts by volume of water.

Leather 4 in a solution of 40 parts of the dry substance consisting of30 parts of the dry substance of cold dissolving quebracho extract, 30parts of mimosa bark extract and 30 parts of chestnut extract and 5parts of myrobalam extract and 5 parts of valex powder in 1000 parts ofwater.

Leather 5 in a solution of parts of pure tannin consisting of theaforesaid mixture in 1000 parts by volume of water.

Leather 6 was not retanned.

Leather 7 is suspended in a solution of 10 parts of the dry substance ofthe retanning agent, described in Example l, in 1000 parts by volume ofwater.

Leather 8 in a solution of 20 parts of the dry substance of the sameretanning agent in 1000 parts by volume of water.

Leather 9 in a solution of 40 parts of the dry substance of the sameretanning agent in 1000 parts by volume of water.

After standing for two days the pieces of leather are removed from thesolution, shortly rinsed, pressed off, set out, oiled off from the grainwith an oxidation inhibiting commercial tanning oil and slowly dried ina dark room.

The dry pieces of leather have the following appearance: Leathers 1, 2,3 have a beautiful light color, are well flexible but nevertheless firm.Leather 6 (not retanned) is essentially darker and more brittle. Thegrain cracks upon more intensely bending. Leathers 4 and 5 are slightlylighter and have markedly better properties than leather 6 but do notreach the quality of leathers l, 2 and 3. Leathers 7 and 8 areapproximately equal to leathers 1, 2 and 3.

The color and grain effect of leather 9 is markedly inferior to that ofleather 3 but superior to that of leather 6.

According to analysis the following substances capable of being washedout were ascertained:

Percent Leather No. 1 5.36 Leather No. 2 6.10 Leather No. 3 6.05 LeatherNo. 4 7.25 Leather No. 5 8.55 Leather No. 6 10.5 Leather No. 7 4.70Leather No. 8 5.28 Leather No. 9 6.02

Example 9.3 pieces of leather of about 10 x 15 cm. are taken fromcomparative positions of the same cow hide described in Example 8. Thepieces of leather are rinsed in flowing water for some minutes. I

Leather No. 1 is oiled off from the grain after setting out well withoxidation inhibiting commercial tanning oil without further treatmentand slowly dried in a dark room.

Leather No. 2 is retanned in 200 parts by volume of water of 40-45 C.(referred to the sammied weight) with a solution of 5 parts of the drysubstance of the retanning agent described in Example 1, which isdissolved in 25 parts by volume fwater, Thesolution oftheretanning agentis added at once, the leather milled for 30 minutes and the pH value ofthe solution adjusted to 5.8 by careful addition of ammonia solution(about The leather is milled in the solution for a further 30 minutes,thereupon removed, shortly rinsed, pressed off and treated withoxidation inhibiting commercial tanning oil in the same manner as thecomparative leather.

Leather No. 3 is treated in equal manner with 5 parts of the drysubstance of the mixture of retanning agents, as described in Example 3,and the tanning solution adjusted to a pH value of 5.9 with ammonia inthe same manner. The leather is further treated as leather No. 2.

After drying the pieces of leather have the following appearance:

Leather 1: Grey-brown color, rather firm leather of moderate graineffect.

Leather 2: The color is markedly lightened and displaced to yellow whilethe grain is of good appearance, the leather is somewhat mellower andmore flexible, no crackiness of the grain.

Leather 3: The appearance is similar to that of leather 2, theflexibility slightly inferior to that of leather 2, the grain effectslightly poorer than leather 2 but markedly better than leather 1.

By analysing the leathers 1, 2 and 3 the following contents ofsubstances capable of being washed out were ascertained:

Example 10.O parts of goat pelt are tanned according to the proceduredescribed in Example 1 of our copending application Ser. No. 295,558,filed June 25, 1952 (now U. S. Patent No. 2,733,977), with parts of thedry substance of the tannin obtainable from resorcinol, ammoniumchloride and formaldehyde as described in Example 33 of our copendingapplication Ser. No. 241,693, filed August 13, 1951 (now abandoned). Theleather is rinsed and set out. The thickness of the leather is measuredat various places.

A solution of 5 parts of the dry substance of the retanning agentemployed in Example 1 in about 40 parts by volume of water is added intwo portions at an interval of 5 minutes into 250-300 parts by volume ofwater. The leather is milled for one hour and the solution adjusted topH 5.8-6.0 as described in Example 1). The leather is shortly rinsed,set out on the table, the thickness measured and oiled oft" from thegrain with a commercial sulfonated fat-liquoring solution. The increasein thickness attained in the retanning process averages 4%. After dryinga leather is obtained which is distinguished from a non-retanned leatherby a greater filling effect, better handle and a color which isdisplaced to yellow.

By carrying out the retanning process with 5 parts of the dry substanceof a commercial, neutralized tannin the increase in thickness averages3%. The filling effect of the dry leather is inferior to that of theleather retanned as above, the color is markedly more reddish.

Example ]].A piece of cow hide tanned with vegetable and synthetictannins by conventional processes and dried is brushed on the grain sidewith a solution of 5 parts of the dry substance of the mixture ofretanning agents, described in Example 3, in 1000 parts by volume ofwater. The tanning solution is applied to the leather by brushing twice;the leather is exposed to air for a short time before the secondbrushing operation. After hanging in the air for a short time theleather thus pretreated is brushed with an aqueous solution of acidleather dyestulfs according to the process generally adapted for theunilateral dyeing of cow hide leather. For comparison a leather wettedwith water only is brushed with the aforesaid dyestutf solution undercomparative con ditions. After drying the leather pretreated with themixture of retanning agents is found to show a markedly deeper shade. Onpolishing this leather shows a more beautiful luster and greaterbrilliance. Furthermore, the pretreatment with the retanning agentresults in inhibiting or preventing the dyestuffs from spewing on to theflesh side of the leather.

Example 12. parts of a leather (calculated as sammied Weight) tannedwith 25 parts of the pure tannin of a vegetable and synthetic mixtureconsisting of 1 part of pure tannin of quebracho wood extract, 1 part ofpure tannin of mimosa bark extract and 2 parts of pure tannin of acommercial synthetic tannin are well rinsed for 10 minutes, set out andshortly suspended in the air. After that the average thickness of theleather is measured at various places. The leather is retanned in 200250parts by volume of water with 5 parts of the dry substance of a tanninobtainable from 4.4-dihydroxydiphenyl sulfone (1 mol), morpholine (4mols) and formaldehyde (4 mols) according to the process of ourcopending application Ser. No. 354,656, filed May 12, 1953 (Example 3).[The retanning agent is prepared by mixing the crystalline4,4'-dihydroxy-diphenyl-sulfone while stirring with the reaction productprepared from the morpholine and formaldehyde (30% solution). Thereaction prodnot of morpholine and aldehyde is prepared by dropping themorpholine into the aldehyde with ice cooling then heating the mixturein a boiling water bath for 1 hour. The precipitated base dissolves uponaddition of 140l50 cc. of concentrated hydrochloric acid] The retanningagent dissolved in about 10 parts by volume of water is added in 2-3portions at intervals of 10 minutes each, the leather milled for afurther 1 /z-2 hours and the solution adjusted to a pH value of about5.5-6 by careful addition of a dilute ammonia solution, as more fullydescribed in Example 1. The leather is milled in the clear solution fora further 30 minutes, removed and horsed up over night. The followingmorning the leather is shortly rinsed, set up well and exposed to air.The thickness of the leather is measured at the same places as before.The leather is oiled off from the grain with a commerical fatliquoringsolution of sulfonated oils and dried. For comparison, a leather tannedwith the above vegetable and synthetic mixture is retanned with 5 partsof the dry substance of a mixture of equal parts of quebracho woodextract and mimosa bark extract in the usual manner. The leatherretanned with the retanning agents has an essentially greater fillingeffect and is of better handle than the leather retanned with thevegetable tannin, the color of the leather is slightly lightened anddisplaced to yellow. The leather retanned with the retanning agent showsan increase in thickness of 7.3% whereas the leather retanned with thevegetable mixture shows a loss of thickness of 2.8%.

Example J3.-l00-parts of the leather employed in Example 12 are retannedwith 5 parts of the dry substance of the retanning agent obtainable from4.4-dihydroxydiphenyl sulfone (1 mol), ethanol amine (4 mols) andformaldehyde (4 mols), as described in our copending application Ser.No. 354,656, May 12, 1953 (Example 10). Following is the procedure ofthat example:

200 cc. of formaldehyde solution (30 percent) is introduced in a thinstream into the mixture grams of 4.4 dihydroxydiphenyl-sulfone and gramsof ethanol amine (94 precent) with stirring and water cooling and themixture is heated in the boiling water bath or refluxed. Thecondensation product obtained is water soluble in all proportions in theform of its base, chloride, sulfate, nitrate and acetate. The tannedleather has an improved filling effect and is more mellow and pliableand of better handle, the color of the leather is lighter, more uniformand markedly displaced to yellow if compared with a leather retannedwith 5 partsof the dry substance of a vegetable mixture of 11 equalparts of quebracho wood extract and mimosa barkextract.

By measuring the thickness of theleather asdescribedin Example 12 theleather treated with the retanning agent is found to shown an increasein thickness of 10.5% whereas the leather retanned with the vegetabletannin shows a loss of thickness of 2.8%.

Example 14.Two pieces of calf pelt of 50 parts each are tanned in 150parts by volume of water as follows:

Pelt 1 is tanned in the usual manner with 4 parts of a 4/ 12 basic,commercial chrome tanning salt containing about 33% of chrome and about3% of sodium sulfate and the pH value is adjusted near the neutralpoint..

Pelt 2 is tanned with a mixture of the following; composition: 9 partsof the dry substance of the mixture of retanning agents described inExample. 3 and 1.0 part of the above commercial trivalent chrome tanningsalt, which is poor in salt, are dissolved in about 40 parts by volumeof water. This solution is introduced into the tanning solution in twoportions at aninterval of 1 hour and the pelt is milled for two days.After that the pH value is adjusted to about 5.8-6.0-by careful additionof ammonia solution (about 5% A tanning solution remains substantiallyclear until the tanning process is complete. Both pieces of leather areshortly. rinsed after tanning and greased with 1 part of'a commercialsynthetic fat liquoring oil.

The pieces of' leather are dried and valuated as follows:

Leather 1 has the typical appearance of achrome leather with the softhandle and the color of normal chrome leather.

Leather 2 has a substantially greater filling effect and is more firmand shows a marked vegetable impression. The leather is of agreeable,yellowish-brown color and shows the green chrome color only in one partof the cutting place.

Example 15.A piece of East Indian cabretta is measured at various placeswith the thickness gauge and the average thickness is ascertained in drycondition. The leather is then well milled in cold water for 30 minutes,set out, the weight is determined and the leather is tanned as follows:100 parts of this wet leather are milled in 250 parts by volume of water(referred to-the drained weight) and retanned with 5 parts of the drysubstance of the mixture of retanning agents employed in Example 3 asdescribed in the preceding examples. After a running time of 75 minutesthe solution is adjusted to a pH value of about 5.8 by careful additionof ammonia solution (about 5%). After reaching this pH value the leatheris circulated for a further 30 minutes, shortly rinsed in fiowing water,set out well and dried. The dried leather is measured again at variousplaces and the average thickness calculated. The increase in thicknessattained in.

the retanning process amounts to 24.5%.

Example 16.-In the same manner as is used in Example 15, 100 parts ofmoist East Indian cabretta are retanned with the retanning agentdescribed in Example 1 and the tanning solution is adjusted to a pH nearthe neutral point. After drying the increase inthickness amounts to28.0%.

Example 17.100 parts of moist East Indian cabretta are retanned in thesame manner as is used in Example 15, in 25 parts by volume of tanningsolution with parts of the dry substance of a retanning agent obtainablefrom 1 mol of o-cresol sulfone, ethanol amine and formaldehyde, asdescribed in Example 4 of our copending application Ser. No. 354,656,filed May 12, 1953, and the pH of the tanning solutionis; adjusted nearthe neutral point; The procedure of reference. Example 4 is'as follows:

139 grams of crude cresol sulfone (prepared, from a crude cresolcontaining 57.2 percent of. o-cresol, 3.8. per- CGIJLOLIIlr-CIBSOI,9.0.percent of. p-cresol and 19.8 percent.

of phenol in the form as it is obtained in the preparation afterremoving volatile ingredients at higher temperatures in vacuo), aremixed with 76 grams of ethanol amine (94 percent) at C. to form ahomogeneous paste. By introducing 128 cc. of formaldehyde solution (30percent) in a thin stream While stirring from 40 C. upwards and heatingthe mixture in the boiling water bath the reaction mixture becomeshomogeneous after a short time. After heating for two hours the mixtureis dissolved in about cc. of concentrated hydrochloric acid at 70-80 C.The reaction product is water soluble in all proportions and reactsweakly Congo-grey. After drying the increase in thickness amounts to22.2%.

Example 18.As described above in Example 15, 100 parts of moist EastIndian cabretta are retanned with 5 parts of the dry substance of aretanning agent obtainable by condensation of 1 mol of o-chlorophenolsulfone, 2 mols of morpholine and 2.2 mols of formaldehyde, as describedin Example 5 of our copending application Ser. No. 354,656, filed May12, 1953. Following is the procedure of reference Example 5:

44 grams of morpholine are added in drops to the suspension of grams ofchlorophenol-sulfone and 50 cc. of formaldehyde solution (30 percent)with stirring and cooling from 20 C. upwards so that the temperaturedoes not exceed 40 C. By heating in the boiling water bath the reactionmixture becomes first homogeneous and resinous after 1 hour. Afterheating for 5 hours the insoluble condensation product is dissolved in50 cc. of hydrochloric acid 1:1 and 13 cc. of concentrated hydrochloricacid at 7080 C. Thereupon the product is water soluble in allproportions and reacts on Congo paper. weakly acid.

In the above reaction the morpholine is replaced by 45 grams of.dimethylamine solution (53 percent). The reaction mixture which ishomogeneous from the start is heated first in the boiling water bath for1 /2 hours and then refluxed for another hour. A portion of thenonconsumed aldehyde is removed by boiling and the evaporated water isreplenished. The insoluble base is dissolved in about 25 cc. ofconcentrated hydrochloric acid. The product is water soluble in allproportions. After neutralizing and drying as usual the increase inthickness amounts to 34.0%.

Example 19.By retanning parts of moist East Indian cabretta with 5 partsof the dry substance of a retanning agent obtainable from 1 mol ofo-chlorophenol sulfone, 2 mols of dimethylamine and 2.25 mols offormaldehyde as described in Example 5 of our copending application Ser.No. 354,656, filed May 12, 1953, an increase in thickness of 36.5% isdetermined after neutralizing and drying. By retanning 100 parts ofmoist East Indian cabretta for comparison with 5 parts of the puresubstance of sumac extract an increase in thickness of 13.8% was foundafter drying.

All the pieces of leather produced as described in the examples byretanning with the cationic tannins are distinguished by extraordinarilybeautiful and good filling properties which excel the filling effect ofthe leather retanned with sumac extract. The color of the leather isgenerally slightly lighter and clearer, the shade mostly displaced toyellow if compared with the East Indian cabretta.

retanned with sumac extract. Furthermore, leather retanned with theretanning agents shows especially beautiful surface luster.

We claim:

1. Retanning process which comprises retanning a previously tannedleather with a tanning liquor containing up to 25% of a salt of acondensation product obtained from sulfones of monohydric phenols withnon-aromatic monoamines and formaldehyde at temperatures about 100 C.

2. The retanning process as claimed in claim 1 wherein thecondensationproduct isobtained from 4.4-dihydroxydiphenyl'sulfone, .ethanolamine'andformaldehyde.

3. The retanning process as claimed in claim 1 wherein References Citedin the file of this patent the condensation product is obtained from4.4'-dihydroxy- UNITED STATES PATENTS diphenylsulfone, morpholine andformaldehyde.

4. The retanning process as claImed in claim 1 wherein g i thecondensation product is obtained from 4.4'-dihydroxy- 5 2127O68 i 1938Iitljddlchiorodlphenylsulfone, morpholine and formalde- 2,129,553Russell Sept. 6, 1938 5. The retanning process as claimed in claim 1wherein g the condensation product is obtained from 4.4'-dihydroxy-2546946 g a 1951 dimethyl-diphenylsulfone, ethanolamrne and formalde- 10ar Oug hyde. FOREIGN PATENTS 615,190 Great Britain Jan. 3, 1949

1. RETANNING PROCESS WHICH COMPRISES TETANNING A PREVIOUSLY TANNEDLEATHER WITH A TANNING LIQUOR CONTAINING UP TO 25% OF A SALT OF ACONDENSATION PRODUCT OBTAINED FROM SULFONES OF MANOHYDRIC PHENOLS WITHNON-AROMATIC MONOAMINES AND FORMALDEHYDE AT TEMPERATURES ABOUT 100*C.